1. Field of the Invention
The present invention relates to an electrophotographic imaging apparatus, and more particularly to a fuser oiling apparatus and the associated method involved with its use and operation.
2. Description of the Related Art
In the electrophotographic process commonly used in imaging apparatus such as laser printers, an electrostatic image is created upon a photosensitive member such as a roll or belt. Visible electroscopic marking particles, commonly referred to as toner, are applied to the electrostatic image on the photosensitive material. Thereafter, the toner is transferred to the desired media, which may include paper, transparency sheets or the like.
The toner image applied to the media is not permanent, however, until the toner is fixed by the application of heat. The toner is elevated in temperature sufficiently to cause constituents of the toner to become tacky, and flow into the pores or interstices between fibers of the media. Upon cooling, the toner again solidifies, causing the toner to adhere to the media. Pressure may be applied to enhance the flow of the toner, and thereby improve the subsequent bonding of the toner to the media.
One approach commonly used for thermally fixing the electroscopic toner images is to pass the media, with the toner image thereon, through a nip formed by thereafter elsewhere in the apparatus. The presence of wayward toner particles in the imaging apparatus can degrade the quality of the printed sheets.
To overcome these problems, fusers of the type described above commonly employ an apparatus for applying a release fluid to the surface of the fuser roll. The release fluid creates a weak boundary between the heated roll and the toner, thereby substantially minimizing the offset of toner to the fuser roll, which occurs when the cohesive forces in the toner mass are less than the adhesive forces between the toner and the fuser roll. Silicone oils having inherent temperature resistance and release properties suitable for the application are commonly used as release fluids. Polydimethylsiloxane is a silicone oil that has been used for this purpose advantageously in the past.
Various methods and apparatuses have been used to supply oil to the fuser hot roll, including oil wicking systems, oil delivery rolls and oil webs. Oil wicking systems include reservoir tanks of the desired release agent or oil, and a piece of fabric wick material having one end mounted in the reservoir and the other end spring biased against the hot roll. Oil from the reservoir is drawn through the fabric wick by capillary action, and is deposited against the roll surface. While a wicking system can be effective in supplying oil to the fuser roll, surface deposit of the oil on the roll can be inconsistent, and the replenishment or replacement of the oil and/or system can be difficult and messy.
A variety of oil delivery roll systems have been used in the past, and include a roll nipped against the hot fuser roll. The oil delivery roll may be either freely rotating against the fuser roll or driven against the roll through a gear train. Oil delivered to the surface of the oil delivery roll is deposited on the hot fuser roll as the rolls rotate against each other. Various structures have been used for providing oil to the surface of the oil delivery roll, including reservoirs at the center of the roll providing oil to the surface through small dispersal holes or via capillary action through the outer material. Felts or metering membranes may be used in the oil delivery roll to control the oil flow through the roll. Another style of such roll is referred to as a web wrapped roll, and includes high temperature paper or non-woven material saturated with oil, and wrapped around a metal core.
Oil web systems include a supply spool of web material, generally being a fabric of one or more layers saturated with the desired oil. A take-up spool is provided for receiving the used web. A web path, commonly including one or more guide rolls, extends from the supply spool to the take-up spool. A portion of the web path brings the web material into contact with the hot fuser roll, either by wrapping a portion of the web around the hot roll, or by utilizing a spring-biased idler roll to nip the web material against the fuser roll. As the fuser roll rotates against the web in contact therewith, oil is transferred from the web to the fuser roll. Periodically, a drive mechanism for the take-up spool activates, rotating the take-up spool and advancing web material from the supply spool to the take-up spool, thereby bringing a fresh section of web material into contact with the fuser roll.
Oil web systems can be used to deliver oil with good uniformity across the fuser roll surface. However, the oil flow is dependent upon the amount of web material brought into contact with the fuser roll over a given period of time. Both, the frequency of indexing and the length of web advancement during indexing influence the amount of oil that is applied to the fuser roll over a given time period. In oil web systems utilized heretofore, the simplified drive systems for the take-up spool have been operated for a consistent duration of time, or for established revolutions or partial revolutions of the take-up spool, at constant intervals throughout the life of the web system. Therefore, as spent material passes onto the take-up spool, and the diameter of the take-up spool increases, the linear length of material brought into contact with the fuser roll increases during each web advancement, thereby increasing the amount of oil deposited on the fuser roll.
Excess oil on the fuser roll has undesirable effects. Since the paper passing through the fuser system generally carries away a portion of the oil deposited on the fuser roll, an excess amount of oil on the fuser roll, when picked up by the paper or other media, can cause an undesirable glossy appearance to the media. In duplexing systems, oil carried on the first printed side can be transferred to other areas of the imaging apparatus, when the media passes again through the apparatus for printing on the second side. Excessive amounts of oil deposited in other sections of the imaging apparatus can decrease print quality, and otherwise produce undesirable operating effects. Additionally, increased linear advancement of the web as the take-up spool diameter increases is wasteful, and shortens the useful life of the oiling system, necessitating replacement and expense.
A further problem can occur in the event of a failure of the drive mechanism for the take-up spool, a web break or other failure of the oil web system to operate properly when web advancement is required. Malfunctions such as these may go unnoticed until operating problems result from the lack of oil application to the fuser roll. The same may occur if the oil web is completely advanced off from the supply spool. If unnoticed, these conditions can result in more severe problems after time.
What is needed is a constant displacement oil web system for an imaging apparatus fuser drum in which a more consistent deposit of oil occurs on the fusing drum than occurs from previously known systems. More specifically, what is needed is an oil web system for an imaging apparatus in which a consistent amount of web material is brought into contact with the fuser drum during a given period of operation, throughout the life of the supply spool.